<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        *{
            margin: 0 !important;
        }
        .test{
            margin: 5px !important;
        }
        div{
            margin: 0
        }
        #app{
            margin: 10px
        }
    </style>
</head>
<body>
    <div id="app" class="test"></div>
</body>
</html>